In the related art, there has been known an optical scanning device installed at an electrophotographic image forming apparatus. The optical scanning device is configured to emit light corresponding to image data at a predetermining writing timing, thereby exposing a photosensitive drum. The optical scanning device has a light source, a deflector that deflects light emitted from the light source and converts the deflected light into scanning light, an image forming lens that forms an image of the scanning light from the deflector on the photosensitive drum, and a synchronization detection sensor that outputs a signal serving as a reference of the writing timing of the image data. The synchronization detection sensor is provided at a predetermining position of a scanning path of the light. Then, the synchronization detection sensor outputs a synchronization detection signal to a controller when the amount of the light received from the light source is equal to or more than a prescribed threshold value. The controller controls a writing timing to an image to the photosensitive drum on the basis of a reception timing of the synchronization detection signal.
In this type of optical scanning device, a scanning speed of the light by the deflector is changed in accordance with printing conditions such as a printing speed and a resolution. In general, as the scanning speed of the light (a printing speed) by the deflector is fast, the amount of the light emitted from the light source is increased. This optical scanning device has a problem that, when the light amount is changed, light detection accuracy by the synchronization detection sensor is reduced. In this regard, in an optical scanning device disclosed in Patent Literature 1, a threshold value of the synchronization detection sensor is changed in accordance with the amount of light emitted from a light source.